1. Field of the Invention
This invention relates to an oxide type solid lubricant which exhibits stable lubricity over a wide temperature range of from room temperature (about 20.degree. C.) to elevated temperatures of about 1,000.degree. C.
2. Description of the Prior Art
A growing need is being felt in a number of advanced fields of technology for a method of lubricating drive components required to operate smoothly in the open air or in an oxidizing atmosphere at temperatures ranging from room temperature (about 20.degree. C.) to elevated temperatures of about 1,000.degree. C.
The mechanical elements of various high-temperature devices such as, for example, the flow path control devices in supersonic jet engine combustion chambers, the mechanical seals in the combination chambers of ceramic gas turbines, and the drive components in MOCVD devices are frequently exposed to temperature changes within the range of from room temperature to elevated temperatures up to 1,000.degree. C. Oil lubrication is not practical at elevated temperatures and no conventional solid lubricant is able to tolerate the impact of heat ranging from room temperature up to elevated temperatures of around 1,000.degree. C. The mechanical elements must therefore be cooled by a suitable means or be isolated from regions heated to elevated temperatures. These special measures inevitably entail complication of design. If a lubricant can be obtained that is stable within such wide temperature range, the device can be simplified without causing a complex or unreasonable design which forces the relocation of high temperature areas and which compels the separation of mechanical elements from each other, since high temperature resistant materials for device construction are available.
Solid lubricants in common use include MoS.sub.2, WS.sub.2, graphite, and PTFE. The temperature ranges in which these non-oxide type solid lubricants can be used effectively have upper limits of about 500.degree. C. at most under oxidative environments. At higher temperatures, these solid lubricants deteriorate by oxidation and lose their lubricity.
In contrast, oxide type solid lubricants are naturally stable and can resist oxidation at elevated temperatures.
FIG. 5 shows the lubricity characteristics (coefficients of friction) of typical oxide type solid lubricants as a function of temperature. In the case of non-oxide type solid lubricants, the upper limit of the working temperature is approximately in the range of 350.degree. C. to 500.degree. C. In the case of oxide type solid lubricants, CoMoO.sub.4 and CoO exhibit high coefficients of friction at room temperature and have working temperatures approximately in the range of 200.degree. C. to 600.degree. C. and B.sub.2 O.sub.3 and NiMoO.sub.4 melt and exhibit lubricity only at elevated temperatures approximately in the range of 500.degree. C. to 600.degree. C. PbO and YBa.sub.2 Cu.sub.3 O.sub.y exhibit relatively high lubricity over a wide temperature range from room temperature to elevated temperatures but nevertheless have upper working temperature limits in the neighborhood of 750.degree. C.
An object of this invention is to provide an oxide type solid lubricant which functions stably in the open air or in an oxidizing atmosphere over a wide temperature range from room temperature to elevated temperatures of about 1,000.degree. C.